Re: [PATCH] bisect: save heap memory. allocate only the required amount

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 25, 2014, 21:14 UTC
Message-ID: <xmqqd2bol1ad.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1408889844-5407-1-git-send-email-arjun024@gmail.com>

Arjun Sreedharan <arjun024@gmail.com> writes:

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> Find and allocate the required amount instead of allocating extra
> 100 bytes
>
> Signed-off-by: Arjun Sreedharan <arjun024@gmail.com>
> ---

Interesting. How much memory do we typically waste (in other words, how big did "cnt" grew in your repository where you noticed this)?

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>  bisect.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/bisect.c b/bisect.c
> index d6e851d..c96aab0 100644
> --- a/bisect.c
> +++ b/bisect.c
> @@ -215,10 +215,13 @@ static struct commit_list *best_bisection_sorted(struct commit_list *list, int n
>  	}
>  	qsort(array, cnt, sizeof(*array), compare_commit_dist);
>  	for (p = list, i = 0; i < cnt; i++) {
> -		struct name_decoration *r = xmalloc(sizeof(*r) + 100);
> +		char name[100];
> +		sprintf(name, "dist=%d", array[i].distance);
> +		int name_len = strlen(name);

Decl-after-stmt.

You do not have to run a separate strlen() for this. The return value from sprintf() should tell you how much you need to allocate, I think.

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> +		struct name_decoration *r = xmalloc(sizeof(*r) + name_len);
>  		struct object *obj = &(array[i].commit->object);
>  
> -		sprintf(r->name, "dist=%d", array[i].distance);
> +		memcpy(r->name, name, name_len + 1);
>  		r->next = add_decoration(&name_decoration, obj, r);
>  		p->item = array[i].commit;
>  		p = p->next;